Don’t forget to select the Regular expresion search mode and to tick the Wrap-around option

Notes :

At beginning of the regex, the modifiers(?s-i) mean that :

The .dot regex character will match any single character ( Standard and EOL chars )

The search is performed in a sensitive way. If you prefer insensitive matches just change that part with (?si) !

Then the part File created by.+?\RMessage log looks, from beginning ( ^ ) of line, for any text, beginning with File created by and ending at the first expression Message log, preceded by a line-break ( \R )

Now, the final part .*?$\R tries to match a range of any character, ending at the nearest end of line ( $ ), and followed with a line-break ( \R )

And, due to the empty replacement zone, all that block of text is, then, simply deleted !